collected in panels at 100 m during 2-unit operation, but was not sampled during initial 3-unit operation 

 because the 100 m panels, which were exposed during May to October, were tampered with by people 

 fishing from boats. Teredo bartschi was not collected at 500 or 1000 m during either 2-unit or 3-unit 

 operation at MNPS. 



In conclusion, since Unit 3 began operation, increased shipworm abundance and increased wood-loss were 

 observed at sites in the MNPS effluent, and during one exposure period, at White Point and Fox Island, 

 which were potentially exposed to the 3-unit thermal plume. Further monitoring will be required to 

 determine whether these changes are related to 3-unit operation, or are expressions of natural variability. 



Fish Ecology Studies 



The operation of MNPS could affect fish assemblages in the Millstone area by increasing mortality at 

 various life history stages (eggs and larvae may be entrained and juveniles and adults may be impinged), 

 or by altering the thermal environment such that the spatial distributions of some fishes change. The 

 report this year emphasizes the comparison of data collected during 2-unit operations to those coUected 

 since the start-up of Unit 3. 



Impingement monitoring at Unit 2 was discontinued on December 11, 1987 because losses were well- 

 documented and all feasible mitigative measures had been investigated. Significant declines in total 

 impingement were found in recent years, which were attributed to physical changes near the Unit 2 intakes 

 and possible changes in water circulation patterns because of the operation of Unit 3. Losses due to 

 impingement by MNPS were reduced with the installation of fish return sluiceways at Units 1 and 3. 



Over 100 fish taxa have been collected in the demersal trawl, shore-zone seine, impingement, and 

 ichthyoplankton sampling programs since 1976. Eight of these taxa were selected for detailed examination 

 due to their prevalence in entrainment or impingement collections or their abundance in the shore-zone 

 area of Jordan Cove, an aiea which may be impacted by the thermal plume. 



The American sand lance was primarily collected as larvae and was a dominant entrained taxon. A decline 

 in larval abundance has occurred since the early 1980s. This decrease was found throughout the region 

 and included the abundance of adults. The decline in larval abundance in the Millstone area was attributed 

 to this area- wide decrease in adult stock size. 



All life history stages of anchovies were very abundant in most of the sampling programs. Adults were 

 present in impingement collections, juveniles were caught by trawl, and eggs and larvae were abundant in 

 entrainment samples. The number impinged declined in recent years, as it has for most species. Based 

 on differential survival from egg to larval stages which was dependent upon initial densities, compensatory 

 mortality was apparent in its early life history. This may mitigate losses of these life stages due to 

 entrainment at MNPS. 



Sticklebacks and Atlantic tomcod were primarily found in impingement samples. The impact of MNPS 

 impingement on sticklebacks has been reduced due to high ( > 70%) survival of individuals returned by 

 sluiceways at Units 1 and 3. There was a marked decrease in Atlantic tomcod numbers impinged at Unit 

 2 since the start-up of Unit 3. This species also exhibits naturally wide fluctuations in numbers because 

 of its reproductive strategy. 



Monitoring Studies, 1986-1987 



